uniform sampler2D m_Texture;
varying vec2 texCoord;
 
void main() {
    vec4 texVal = texture2D(m_Texture, texCoord);
    //float g = max(texVal.r,max(texVal.g,texVal.b));
    float g = texVal.r * 0.21 + texVal.g * 0.71 + texVal.b * 0.07;
    gl_FragColor = vec4(g, g, g, 1.0);
}